in small stakes NL as a rule of thumb 20 x BuyIn is considerd to be good bankroll management. when you've got to 200NL and above, you probably want a bigger bankroll than 20 BuyIns.

As givememyleg mentioned: for 25NL you'll need about $500

Good post for Bankroll Management: http://www.flopturnriver.com/phpBB2/...poker-4971.htm